The present invention relates generally to a disc drive assembly. In particular, the present application relates to a shock limiting suspension for a magnetic read-write head in a disc drive assembly.
Disc drives of systems are known which read data from a disc surface during operation of a disc drive. Typically, such disc drive systems include magnetic disc drives and optical disc drive systems. Generally, discs are rotated for operation of the disc drive via a spindle motor to position for reading data from or writing data to selected portions or tracks on the disc surface.
The read-write head generally includes an air bearing surface, which floats or flies above the disc surface in a known manner. Generally, the slider flies with a positive pitch angle at which the leading edge of the slider flies at a greater distance from the disc surface than the trailing edge via a suspension assembly, which includes a load beam and a gimbal. The slider is coupled to the load beam via a gimbal. The load beam applies a load force to the slider via a dimple. The dimple defines an access about which the slider pitches and rolls via the gimbal. The slider is preferably resilient in the pitch and roll direction to enable the slider to follow the topography of the disc based on the hydrodynamic lifting force caused by the disc rotation.
Generally, the gimbal permits the air bearing slider to pitch and roll as the slider flies above the disc surface. It is important to maintain the proximity of the slider relative to the disc surface during operation. In a typical disc drive, a magnetic transducer element is carried on the slider to write data to the disc surface.
Depending on the mass and stiffness of the suspension assembly, including the gimbal and the load beam, external vibration may excite the load beam and gimbal at a resonant frequency. Thus, the input motion or external vibration may be amplified substantially, causing unstable misalignment of the slider relative to the disc surface. Such misalignment may result in data loss and/or damage to the disc surface.
External vibration or excitation of the suspension assembly and slider may introduce varied motion of the slider and suspension assembly. Depending on the nature and frequency of the excitation force, the slider and suspension assembly may cause torsional mode motion, sway mode vibration and bending mode resonance. Torsional mode motion relates to rotation or twisting of the suspension assembly about an in-plane axes. Bending mode resonance essentially relates to up-down motion of the suspension assembly relative to the disc surface. Sway mode vibration relates to in-plane lateral motion and twisting. It is very important to limit resonance motion to assure stable fly characteristics for the slider. In particular, it is important to control the torsion and sway mode resonance, since they produce a transverse motion of the slider, causing head misalignment with respect to the data tracks of the disc surface.
Generally, the resonance frequency of the suspension assembly is related to the stiffiness or elasticity and the mass of the suspension system. Thus, it is desirable to design a suspension system, which limits the effect of sway mode and torsion mode resonance in the operating frequencies of the disc drive, while providing a suspension design which permits the slider to pitch and roll relative to the dimple.
Deflection limiters are beneficial for multiple reasons. During a shock event, such as dropping the disc drive or the lap top computer, the mass of the head can pull the gimbal away from the load beam if there is not deflection limiter. The shock event can induce stress in the gimbal. This stress may be enough to bend the gimbal and result in dimple separation and/or changes to the pitch and roll static angle (attitude) of the gimbal. A deflection limiter is designed to prevent separation of the gimbal by insuring that the deflection is not large enough to cause the stress to reach the gimbal's yield point, which could cause gimbal separation resulting in disc drive failure.
Such deflection limiters structures are broadly known. Generally, they are designed to either prevent excessive movement during shock events such as the jarring or dropping of a computer, or to prevent non-operational damage to the suspension-gimbal structure.
Generally, there are two ways in which to introduce a shock limiter to a disc drive structure: features are presented on the load beam to engage the gimbal and limit the excessive motion during shock events, or features are presented on the gimbal to engage the load beam to prevent excessive motion during a shock event.
In the field of suspension technology for magnetic disc drives, stainless steel is typically used as the support structure for the slider. A typical configuration consists of an etched gimbal ring, which is welded to the suspension load beam. A circuit is routed over or adjacent to the steel gimbal to provide an electrical connection to the slider. The assembly is cantilevered from the load beam and pre-loaded against a dimple, which protrudes from the load beam. For robustness, a hook is formed in the steel gimbal sheet and is interleaved through an opening in the load beam. This feature serves as the “limiter”.
This type of limiter is relatively simple to incorporate into a Load/Unload mobile drive application due to the available material around the load point and slider necessary to support the lift tab feature at the distal end. However, incorporating such a limiter into a non-Load/Unload or a contact start stop (CSS) design becomes difficult because of a number of factors: material availability, resonance requirements, tolerance “stack-up”, slider bonding area, clearance for assembly processes, attitude adjustability, and robustness.
In non-Load/Unload and CSS designs, there is insufficient available material to incorporate the limiter engagement feature. Specifically, the load beam tip is narrow and the load point is typically coincident with the end of the beam, leaving little extra material from which to form the limiter engagement feature.
Resonance requirements of the head gimbal assembly dictate that the structural mass at the load arm tip must be minimized. Specifically, it is desirable to minimize the mass added to the structure. If mass must be added, it is desirable to keep the added mass as close as possible to the center line or axis of the structure in order to maintain the equilibrium or balance of the structural mass. By minimizing the mass and by keeping the added mass near the center line, the overall resonance performance of the structure is enhanced.
With respect to tolerance “stack up”, incorporation of a limiting feature internal to the load beam (such as the interleaved hook through an opening in the load beam) requires clearance for clamping, forming, and welding, and other steps of the fabrication and assembly processes.
Additionally, when the limiter is interleaved through an opening in the load beam, material must be removed from the load beam to provide the opening. This, in turn, impacts the resonance performance of the system as a whole. Additionally, removal of material from the gimbal/tongue area to provide the limiter structure necessarily reduces the size of the bonding area available for attaching the slider to the gimbal.
Finally, the various limiters in the prior art typically impose structural limitations on the disc drive structure, such as allowing clearance for gold ball bonding processes and limiting adjustability of the pitch and roll static attitude during assembly.
Therefore, it is desirable to have a robust shock limiter that maintains the narrow profile of the load beam and that adds little material in a balanced arrangement close to the center axis (center of mass) of the suspension. Moreover, it is desirable that the gimbal interleave with the load beam without requiring an opening in the load beam and without removing much material from the gimbal in the bonding area. Finally, it is desirable to have a robust shock limiter that maintains pitch and roll static attitude adjustability during assembly.